The invention relates to that concept of winemaking introduced by U.S. Pat. No. 3,528,817 whose disclosure is herein incorporated by reference. The concept embodied therein is that of reducing winemaking time from a matter of years to approximately three weeks by the pressure containment of carbon dioxide and other gaseous products evolved during fermentation in open communication with the fermentable mixture. The aforesaid prior patent relates to small, home winemaking kits and the pressure containment is effected by an energy storing resilient bladder.
It is the purpose of this invention to extend the concept to large scale commercial operations.
The following detailed discussion of those conclusions derived from an extended practice of the patented invention as applied to small home winemaking kits will facilitate an understanding of the manner in which the concept may be adapted to commercial winemaking. As pointed out in the aforesaid patent, the precise chemical reactions and theoretical considerations underlying the fantastic acceleration in winemaking time were not completely understood at that time; it being clear, however, that pressure containment of the gaseous products evolved during fermentation in open communication with the fermentable mixture did produce the desired result.
It became apparent from the practice of the patented invention that the excellent quality of the wine obtained thereby in approximately three weeks could not be due solely to an accelerated fermentation time since the concept of "aging" is essential to quality wine. It was therefore assumed that some process was taking place concomitantly with the fermentation process which produced either some unknown reaction resulting in a palatable product indistinguishable from time aged wine or that actual aging was also taking place at a fantastically accelerated rate. The latter is now known to be the case and it is thought that fermentation proceeds substantially to completion within 7-10 days while the remainder of the time is taken up with the aging process.
It will be recalled from the prior patent disclosure that the initial fermentation rate is extremely rapid which appears to be explainable, at least in the first instance, by the fact that the apparatus is evacuated thus providing a maximal partial pressure differential across the liquid-gas interface. This initial situation is radically altered, almost immediately, as the evolved fermentation gases fill the container and commence to extend the bladder. The fermentation rate then increases dramatically which was thought to be explainable by the fact that the evolved gases are continually being driven back into solution as a function of their increasing partial pressures across the gas-liquid interface, to, in effect, catalyze the fermentation reaction. The increasing partial pressures exerted by the evolved gases is, of course, a direct function of bladder distension which, in turn, is a function of fermentation time. During the initial portions of the fermentation period, partial pressures across the liquid-gas interface, i.e. the evolving gas pressures greatly exceed those across the gas-liquid interface, i.e. the gases returning into solution. At a point in time just prior to substantial completion of the fermentation period (7-10 days) the gases passing into and out of solution reach equilibrium and it is at this point in time when the bladder has reached its maximum distension thereby containing a maximum volume of evolved gases and exerting maximum pressure thereon. Although fermentation is thought to continue, to some degree; the equilibrium has shifted and net mass flow is back into solution as the bladder starts to contract. This situation obtains with the bladder contracting until the winemaking process is substantially complete at which time substantially all gas flow is across the gas-liquid interface and into solution. It is the latter period of the home winemaking process, with the bladder collapsing, which is now thought to constitute a distinct aging period.
Like the fantastically accelerated fermentation rate, aging of the fermented mixture is also greatly accelerated. With recognition of the fact of aging and awareness of the individual factors contributing to aging, it was found that the same could be controlled, in small home winemaking kits, in the manner disclosed in applicant's co-pending application Ser. No. 245,442 filed Apr. 19, 1972.
Briefly, it is the volume of evolved gases which are driven back into solution following the initial fermentation period that controls aging. It is assumed, though not yet verified, that the aging process is taking place to some small degree during the fermentation period of the first few days but that the great proportion of the aging process takes place following substantial cessation of fermentation. In any event it appears clear that aging is a direct function of the integral of instantaneous gaseous volume absorbtion over a time interval extending approximately between the maximum bladder extention and collapse of the same.
Surprisingly, overaging was the primary problem plaguing the successful practice of the prior patented invention. Overaged wine is that whose end acid concentration is too high and is characterized by a fruity or vinegary taste (depending upon the particular wine and degree of aging) and a generally brownish coloration. For reasons which were not completely understood prior to extensive testing on a commercial basis, substantially complete evacuation of the apparatus (to approximately 0.1 atm. for example) prior to the commencement of fermentation was known to be critical to the accelerated production of palatable, properly aged wines. Similarly, it was known that the apparatus must remain sealed with respect to atmosphere during the entire fermentation and aging periods.
Thus, the conceptual criteria derived from extended observation and experimentation based upon the small winemaking kits employing resilient bladders to effect the desired pressure containment which it is the purpose of this invention to extend to commercial winemaking operations are threefold:
(1) Initial evacuation of the apparatus;
(2) Pressure control of fermentation gases in contact with the fermenting mixture to accelerate fermentation; and
(3) Volume control of fermentation gases driven back into solution during the aging period to control aging.
The large scale commercial operations contemplated herein may involve batch containers or fermenters whose volumetric capacity may exceed a 100 gallon batch by 20%-100% or a 100,000 gallon batch by 20%-100%. Stated differently, the volumetric capacity of the batch container must exceed the initial volume of the fermentable mixture but the excess volume may vary within wide limits. It is immediately apparent that the use of a resilient bladder to control volume and pressure would be an impractical approach. Moreover, the minor variations in quality control that are permissible for home winemaking units involving small batches where the control is exercised more or less empirically as a function of expanded bladder size cannot be tolerated in commercial winemaking operations for many reasons, one of the more obvious of which is the financial loss that would be entailed if even one 100,000 gallon batch were ruined. A critical problem in connection with large capacity fermenters which does not exist in small capacity winemakers, if the accelerated winemaking time is to be maintained, is one of surface area exposure and it is this precise point that requires radical departure from the aforesaid concepts applicable to small, home winemakers. Thus, while fermentation gases may evolve freely from a one (1) gallon batch and the returning gases move more or less readily into homogenous solution with the small volume fermentable mixture; it will be appreciated that the far lesser percentage surface area exposure in a 100,000 gallon batch or even in a 100 gallon batch would insure lesser proportional reaction rates. Since it is desired to maintain the very short winemaking periods achieved with the small units; it is necessary to either further increase the previously noted reaction rates or increase surface area exposure. Actually, both of these are effected as a function of two conceptual changes in the method of operation previously outlined for small winemaking units, i.e.
(1) immediately charging the batch container from a separate source of fermentation gases as opposed to sole reliance upon those gases evolved from the fermenting mixture; and
(2) maintaining the fermentable mixture in a substantially frothed condition during a major portion of the winemaking process.
Although aerobically produced fermentation gases consist mostly of carbon dioxide, the objectives of the invention are not achieved by charging with CO.sub.2 for the obvious reason that the anaerobically produced microorganism strains and acids upon which the present invention depends are not present and the product resulting from such effort is not palatable. As used herein, the term "anaerobic" is deemed to mean the substantial absence of elemental oxygen. Efforts to date have failed to uncover a suitable substitute for fermentation gases produced in a nonoxidizing atmosphere though it is theorized that if the same could be synthesized, the resultant wine would be palatable.